package com.lagou.sqlSession;

import com.lagou.pojo.Configuration;
import com.lagou.pojo.MappedStatement;

import java.lang.reflect.*;
import java.util.List;

public class DefaultSqlSession implements SqlSession {

    private Configuration configuration;

    public DefaultSqlSession(Configuration configuration) {
        this.configuration = configuration;
    }

    @Override
    public <E> List<E> selectList(MappedStatement mappedStatement, Object... params) throws Exception {
        //将要去完成对simpleExecutor里的query方法的调用
        SimpleExecutor simpleExecutor = new SimpleExecutor();
        List<Object> list = simpleExecutor.query(configuration, mappedStatement, params);

        return (List<E>) list;
    }

    @Override
    public <T> T selectOne(MappedStatement mappedStatement, Object... params) throws Exception {
        List<Object> objects = selectList(mappedStatement, params);
        if (objects.size() == 1) {
            return (T) objects.get(0);
        } else {
            throw new RuntimeException("查询结果为空或者返回结果过多");
        }


    }

    @Override
    public int writeDatabase(MappedStatement mappedStatement, Object... params) throws Exception {
        //将要去完成对simpleExecutor里的query方法的调用
        SimpleExecutor simpleExecutor = new SimpleExecutor();
        return simpleExecutor.write(configuration, mappedStatement, params);
    }

    @Override
    public <T> T getMapper(Class<?> mapperClass) {
        // 使用JDK动态代理来为Dao接口生成代理对象，并返回

        Object proxyInstance = Proxy.newProxyInstance(DefaultSqlSession.class.getClassLoader(), new Class[]{mapperClass},
                (proxy, method, args) -> {
                    // 底层都还是去执行JDBC代码 //根据不同情况，来调用selctList或者selectOne
                    // 准备参数 1：statmentid :sql语句的唯一标识：namespace.id= 接口全限定名.方法名
                    // 方法名：findAll
                    //System.out.println(proxy);
                    String methodName = method.getName();
                    String className = method.getDeclaringClass().getName();

                    String statementId = className + "." + methodName;

                    // 准备参数2：params:args
                    // 获取被调用方法的返回值类型
                    Type genericReturnType = method.getGenericReturnType();
                    MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
                    switch (mappedStatement.getSqlCommand().getType()){
                        case SELECT:
                            // 判断是否进行了 泛型类型参数化
                            if (genericReturnType instanceof ParameterizedType) {
                                return selectList(mappedStatement, args);
                            }
                            return selectOne(mappedStatement, args);

                        case INSERT :
                            return writeDatabase(mappedStatement,args);
                        case UPDATE:
                            return writeDatabase(mappedStatement,args);
                        case DELETE:
                            return writeDatabase(mappedStatement,args);
                        case UNKNOWN:

                    }
                    throw new RuntimeException();

                });

        return (T) proxyInstance;
    }


}
